1. Field of the Invention
The invention relates generally to the art of axle/suspension systems for heavy-duty vehicles. More particularly, the invention relates to air-ride axle/suspension systems for heavy-duty vehicles which utilize an air spring to cushion the ride of the vehicle. More specifically, the invention is directed to an air spring of a heavy-duty vehicle air-ride axle/suspension system, in which the air spring is optimized to provide damping characteristics to the air spring and in turn to the axle/suspension system based upon the volume of the bellows chamber of the air spring, the volume of the piston chamber of the air spring, and the size(s) of one or more openings formed in the air spring between and communicating with the bellows chamber and the piston chamber. Even more specifically, the flow of air between the piston chamber and the bellows chamber through the openings located between the piston chamber and the bellows chamber of the air spring provides viscous damping to the air spring.
2. Background Art
The use of air-ride trailing and leading arm rigid beam-type axle/suspension systems has been very popular in the heavy-duty truck and tractor-trailer industry for many years. Although such axle/suspension systems can be found in widely varying structural forms, in general their structure is similar in that each system typically includes a pair of suspension assemblies. In some heavy-duty vehicles, the suspension assemblies are connected directly to the primary frame of the vehicle. In other heavy-duty vehicles, the primary frame of the vehicle supports a subframe, and the suspension assemblies connect directly to the subframe. For those heavy-duty vehicles that support a subframe, the subframe can be non-movable or movable, the latter being commonly referred to as a slider box, slider subframe, slider undercarriage, or secondary slider frame. For the purpose of convenience and clarity, reference herein will be made to main members, with the understanding that such reference is by way of example, and that the present invention applies to heavy-duty vehicle axle/suspension systems suspended from main members of primary frames, movable subframes and non-movable subframes.
Specifically, each suspension assembly of an axle/suspension system includes a longitudinally extending elongated beam. Each beam typically is located adjacent to and below a respective one of a pair of spaced-apart longitudinally extending main members and one or more cross members which form the frame of the vehicle. More specifically, each beam is pivotally connected at one of its ends to a hanger which in turn is attached to and depends from a respective one of the main members of the vehicle. An axle extends transversely between and typically is connected by some means to the beams of the pair of suspension assemblies at a selected location from about the mid-point of each beam to the end of the beam opposite from its pivotal connection end. The beam end opposite the pivotal connection end also is connected to an air spring, or its equivalent, which in turn is connected to a respective one of the main members. A height control valve is mounted on the main member or other support structure and is operatively connected to the beam and to the air spring in order to maintain the ride height of the vehicle. A brake system and one or more shock absorbers for providing damping to the axle/suspension system of the vehicle also are mounted on the axle/suspension system. The beam may extend rearwardly or frontwardly from the pivotal connection relative to the front of the vehicle, thus defining what are typically referred to as trailing arm or leading arm axle/suspension systems, respectively. However, for purposes of the description contained herein, it is understood that the term “trailing arm” will encompass beams which extend either rearwardly or frontwardly with respect to the front end of the vehicle.
The axle/suspension systems of the heavy-duty vehicle act to cushion the ride, dampen vibrations and stabilize the vehicle. More particularly, as the vehicle is traveling over the road, its wheels encounter road conditions that impart various forces, loads, and/or stresses, collectively referred to herein as forces, to the respective axle on which the wheels are mounted, and in turn, to the suspension assemblies that are connected to and support the axle. In order to minimize the detrimental effect of these forces on the vehicle as it is operating, the axle/suspension system is designed to react and/or absorb at least some of them.
These forces include vertical forces caused by vertical movement of the wheels as they encounter certain road conditions, fore-aft forces caused by acceleration and deceleration of the vehicle, and side-load and torsional forces associated with transverse vehicle movement, such as turning of the vehicle and lane-change maneuvers. In order to address such disparate forces, axle/suspension systems have differing structural requirements. More particularly, it is desirable for an axle/suspension system to be fairly stiff in order to minimize the amount of sway experienced by the vehicle and thus provide what is known in the art as roll stability. However, it is also desirable for an axle/suspension system to be relatively flexible to assist in cushioning the vehicle from vertical impacts, and to provide compliance so that the components of the axle/suspension system resist failure, thereby increasing durability of the axle/suspension system. It is also desirable to dampen the vibrations or oscillations that result from such forces. A key component of the axle/suspension system that cushions the ride of the vehicle from vertical impacts is the air spring, while a shock absorber typically provides damping characteristics to the axle/suspension system.
The typical air spring of the type utilized in heavy-duty air-ride axle/suspension systems includes three main components, a flexible bellows, a piston and a bellows top plate. The bellows is typically formed from rubber or other flexible material, and is operatively mounted on top of the piston. The piston is typically formed from steel, aluminum, fiber reinforced plastics or other rigid material and is mounted on the rear end of the top plate of the beam of the suspension assembly, by fasteners, which are generally well known in the art. The volume of pressurized air, or “air volume”, that is contained within the air spring is a major factor in determining the spring rate of the air spring. More specifically, this air volume is contained within the bellows and, in some cases, the piston of the air spring. The larger the air volume of the air spring, the lower the spring rate of the air spring. A lower spring rate is generally more desirable in the heavy-duty vehicle industry because it provides a softer ride to the vehicle during operation. Typically, the piston either contains a hollow cavity, which is in communication with the bellows and which adds to the air volume of the air spring by allowing unrestricted communication of air between the piston and the bellows volumes, or the piston has a generally hollow cylindrical-shape and does not communicate with the bellows volume, whereby the piston does not contribute to the air volume of the air spring. The air volume of the air spring is in fluid communication with an air source, such as an air supply tank, and also is in fluid communication with the height control valve of the vehicle. The height control valve, by directing air flow into and out of the air spring of the axle/suspension system, helps maintain the desired ride height of the vehicle.
Prior art air springs such as the one described above, while providing cushioning to the vehicle cargo and occupant(s) during operation of the vehicle, provide little if any damping characteristics to the axle/suspension system. Such damping characteristics are instead typically provided by a pair of hydraulic shock absorbers, although a single shock absorber has also been utilized and is generally well known in the art. Each one of the shock absorbers is mounted on and extends between the beam of a respective one of the suspension assemblies of the axle/suspension system and a respective one of the main members of the vehicle. These shock absorbers add complexity and weight to the axle/suspension system. Moreover, because the shock absorbers are a service item of the axle/suspension system that will require maintenance and/or replacement from time to time, they also add additional maintenance and/or replacement costs to the axle/suspension system.
The amount of cargo that a vehicle may carry is governed by local, state, and/or national road and bridge laws. The basic principle behind most road and bridge laws is to limit the maximum load that a vehicle may carry, as well as to limit the maximum load that can be supported by individual axles. Because shock absorbers are relatively heavy, these components add undesirable weight to the axle/suspension system and therefore reduce the amount of cargo that can be carried by the heavy-duty vehicle. Depending on the shock absorbers employed, they also add varying degrees of complexity to the axle/suspension system which is also undesirable.
Certain prior art air springs have attempted to provide damping characteristics to the air spring by placing valves between the bellows and piston chambers of the air spring. Still other prior art air springs have attempted to provide damping characteristics to the air spring by forming an opening between the bellows and piston chambers of the air spring which is partially covered by rubber flaps mounted adjacent to the opening in order to provide damping characteristics to the air spring. Still other prior art air springs have included a large opening or openings between the bellows and the piston in order to allow full, unrestricted, communication of air between the two volumes to increase the air volume and hence reduce the spring rate of the air spring which provides a softer ride to the vehicle during operation. However, the prior art air springs that include valves are complicated and require valve components that can break down over time requiring expense and time to replace. Prior art air springs that have included openings with rubber flaps typically restrict some air movement in one direction but allow free air flow in the opposite direction. Moreover, these rubber flaps, like the valves, are additional components within the air spring that can wear, requiring costly repairs and/or maintenance. In addition, these prior art air springs, which include openings between the bellows and the piston, do not consider the volume of the bellows chamber, the volume of the piston chamber or the size and/or number of openings formed between and communicating with the bellows chamber and the piston chamber in order to provide improved damping characteristics to the air spring.
The air spring with damping features for heavy-duty vehicles of the present invention, overcomes the problems associated with prior art air springs by providing certain structural relationships between the bellows chamber, piston chamber and openings formed between and communicating with the bellows and piston chambers, resulting in optimization of the damping characteristics of the air spring, while using generally fewer parts than prior art air springs that utilize valves, rubber flaps and the like. The air spring with damping features for heavy-duty vehicles includes tuning certain structural components of the air spring in order to optimize or find the “sweet spot” for the damping characteristics of the air spring for a given application, based upon piston chamber volume, bellows chamber volume and the size, shape, length, and/or number of openings formed between and communicating with the bellows chamber and the piston chamber of the air spring. By providing an air spring for heavy-duty vehicles having optimized damping characteristics, the shock absorber of the axle/suspension system can be eliminated or its size reduced, reducing complexity, saving weight and cost, and allowing the heavy-duty vehicle to haul more cargo. Moreover, elimination of the shock absorbers, valves and/or rubber flaps potentially eliminates costly repairs and/or maintenance costs associated with these more complicated systems.